Various active safety systems have been developed to prevent injury to a user if they approach or come into contact with a dangerous portion of a machine. Such systems typically include two components: a detection portion and a braking portion. U.S. Pat. Nos. 3,785,230 and 4,026,177 to Lokey describe one such system. The system of Lokey uses a detection system that detects dangerous proximity of a part of a user's body. The system relies on a radio-frequency proximity detection. When the detection system detects a dangerous condition, a solenoid is triggered to shift a brake into engagement with the blade. Because the system of Lokey does not wait for contact to occur, the relatively low brake actuation speed provided by a direct-acting solenoid may be adequate to prevent injury. However, in a system that relies on contact detection, the braking time must be minimized. Even in proximity-based systems, it is beneficial to reduce braking time to minimize the chance of injury.
In a system that utilizes a brake to stop the machine, the spacing between the brake and the portion of the machine to be braked—typically a cutter or saw blade—can lead to significant delays in brake action. For instance, a solenoid may supply a few pounds of force over an eighth of an inch. With a relatively light brake of 150 g, a solenoid capable of generating 10 pounds of force takes five milliseconds to move the brake an eighth of an inch. Thus, it is important that the brake be located as close as possible to the portion of the machine to be stopped. However, where the brake contacts the blade directly, the position of the brake may need to be adjustable to accommodate variations in blade size.